The present invention relates generally to the field of instrumentation and systems for the spine, and more particularly to instrumentation and systems for use in treatment of various pathologies of the cervical spine.
As with any bony structure, the spine is subject to various pathologies that compromise its load bearing and support capabilities. Such pathologies of the spine include, for example, degenerative diseases, the effects of tumors and, of course, fractures and dislocations attributable to physical trauma. Spinal surgeons have addressed these problems using a wide variety of instrumentation in a broad range of surgical techniques. The use of elongated rigid plates has been helpful in the stabilization and fixation of the lower spine, most particularly in the thoracic and lumbar spine. These same plating techniques have found some level of acceptance by surgeons specializing in the treatment of the cervical spine.
The cervical spine can be approached either anteriorly or posteriorly, depending upon the spinal disorder or pathology to be treated. Many well-known surgical exposure and fusion techniques of the cervical spine are described in the publication entitled Spinal Instrumentation, edited by Drs. Howard An and Jerome Cotler. This text also describes instrumentation that has been developed in recent years for the cervical spine. Plating systems have become predominant for providing internal instrumentation in techniques that achieve fusion of the cervical spinal from an anterior approach.
During the development of cervical plating systems, particularly for the anterior approach, various needs have been recognized. For example, the system should provide strong mechanical fixation that can control movement of each vertebral segment. The system should be able to withstand axial loading and continuity with each of the three columns of the spine. The system should also be able to maintain stress levels below the endurance limits of the plate material, while at the same time exceeding the strength of the anatomic structures or vertebrae to which the plating system is engaged. The thickness of the system should be small to lower its prominence, particularly at the smaller spaces of the cervical spine. Also, the screws used to connect the plate to the vertebrae must not loosen over time or back out from the plate.
While the plating system should satisfy certain mechanical requirements, the system should also satisfy certain anatomic and surgical considerations. For example, the cervical plating system should minimize the intrusion into the patient and reduce the trauma to the surrounding soft tissue. This is particularly important in such procedures that relate to the cervical spine because the complications can be very devastating, such as injury to the brain stem, spinal cord, or vertebral arteries. It has also been found that the optimum plating system permits placement of more than one screw in each of the instrumented vertebrae. Also, the system should be designed to contact the vertebrae for greater stability.
Many spinal plating systems have been developed in the last couple of decades to address some of the needs and requirements for cervical fixation systems. However, even with the more refined plating system designs, there still remains a need for a system that effectively addresses the requirements for such a system.
There is also a need for a plating system that addresses procedures designed to achieve fusion of the cervical spine. In cases where a graft or implant is implanted to maintain a disc space and/or replace one or more diseased vertebral bodies, it is desirable to increase the rate of fusion and incorporation of the graft or implant into the spine. A plating system that allows pre-loading of the graft or implant and/or provides continual loading thereafter is preferred.
While the prior art plating systems relating to cervical plating systems are steps in the right direction, there remains a need for additional improvements. The present invention is directed to satisfying these needs, among others.
The present invention contemplates a system for anterior fixation of the spine that utilizes an elongated fixation plate. In one aspect of the invention, the plating system promotes fusion and incorporation of a graft or implant in a spinal column portion. The plating system provides continual loading of the graft or interbody implant. In another aspect, the plating system allows a compressive load to be applied to the spinal column portion. This pre-loading and continual loading avoids stress-shielding and promotes fusion and incorporation of the graft or implant into the spinal column portion.
In one aspect of the invention, the fixation plate has a first end with a pair of holes. Bone engaging fasteners extend through the holes to rigidly secure the plate to a first vertebra. A second end of the plate is provided with a pair of slots through which bone engaging fasteners extend for engagement with a second vertebra. The bone engaging fasteners extending through the slots are translatable in the slots to allow settlement and compression of the second vertebra with respect to the first vertebra. In a preferred embodiment, the plating system includes a retainer assembly that prevents fastener back out.
According to another aspect of the invention, a bone fixation system for a spinal column segment is provided. The bone fixation system includes a plate with a central axis, a length between a first end and a second end, and top and bottom surfaces. The plate defines a plurality of first openings and a plurality of second openings between the top and bottom surfaces. At least one of the plurality of first openings is positioned adjacent the first end of the plate and defines a circular hole though the plate. At least one of the plurality of second openings is positioned adjacent the second end of the plate and defines a slotted hole having a first width and a first length adjacent the bottom surface. A number of bone engaging fasteners extend through the first and second openings. Each bone engaging fastener has a threaded shank and an enlarged head. The fastener has a substantially cylindrical portion with a third diameter that interfaces with the plate in the first opening such that the fastener inserted in the first opening assumes a fixed orientation with the plate. The head of said bone engaging fastener inserted into the second opening is translatable along the length of the second opening to maintain compression of the spinal column portion.
In another aspect of the invention, a bone fixation system for a spinal column portion is provided. The bone fixation system includes a plate with a length along a central axis that extends between a first end and a second end. The plate has a top surface and a bottom surface and defines a plurality of first and second openings between the surfaces. At least a pair of the first openings is positioned adjacent the first end, and the first openings define a circular opening having a first diameter. At least a pair of the second openings is positioned adjacent the second end, and the second openings define a slot having a first width and a first length. A number of bone engaging fasteners with an elongated threaded shank and an enlarged head are provided. The bone engaging fasteners extend through the first and second holes from the top surface. A retainer assembly retains the bone engaging fasteners in the first and second openings. In one form, the retainer assembly includes a washer having a length that substantially corresponds to the length of the plate.
In yet another aspect of the invention, a bone fixation system for a spinal column segment is provided. The system includes four bone engaging fasteners that have an enlarged head and a threaded shank. An elongated plate has a length extending between a first end and a second end sized to span between at least two vertebrae. The plate defines one pair of holes adjacent the first end and one pair of slots adjacent the second end. Each of the holes and the slots are configured to receive the threaded shank of a corresponding one of the bone engaging fasteners therethrough to engage the plate to the vertebrae. The bone engaging fasteners extend through the pair of holes to fix the plate to the first vertebra. Bone engaging fasteners extend through the pair of slots to secure the plate to the second vertebra. The bone engaging fasteners axially translate in the slots to maintain compression on the spinal column portion.
In a further aspect of the invention, a bone fixation system for a spinal column portion is provided. The system includes six bone engaging fasteners that each have an enlarged head and a threaded shank. An elongated plate extending between a first end and a second end has a length sized to span between at least three vertebrae. The plate defines one pair of holes over a first vertebra, one pair of slots over a second vertebra, and one pair of intermediate slots over a third vertebra intermediate the first and second vertebrae. The holes and the slots are configured to receive the threaded shank of the bone engaging fasteners therethrough. The bone engaging fasteners extend through the pair of holes to fix the plate to the first vertebra. The bone engaging fasteners extend through the slots to secure the plate to the second vertebra. The bone engaging fasteners axially translate in the slots to maintain compression on the spinal column portion. The surgeon can optionally place bone engaging fasteners in the intermediate slots to engage the plate to the third vertebra.
In another aspect of the invention, there is provided a retainer assembly for an elongated plate that extends between at least two vertebrae. The retainer assembly includes a washer having at least one tapered aperture. The washer is translatable between a locked position and an unlocked position by threading a locking fastener into the tapered aperture.
In another aspect of the invention, there is provided a retainer assembly for an elongated plate that extends between at least two vertebrae. The plate defines a number of openings for insertion of bone engaging fasteners to attach the plate to the at least two vertebrae. The plate further includes a first fastener bore in the plate adjacent at least one of the openings positioned over the first vertebra and a second fastener bore in the plate adjacent at least one of the openings positioned the second vertebra. The retainer assembly includes a washer that defines at least a first aperture adjacent the at least one opening positioned over the first vertebra and a second aperture adjacent the at least one opening positioned over the second vertebra. A locking fastener for each of the apertures in the washer has an elongated shank extending through the aperture configured to engage the fastener bore of the plate. The washer is movable between a first position where the bone engaging fasteners are insertable into each of the at least one openings and a second position where the washer has a surface configured to contact the head of a bone engaging fastener extending through the at least one opening positioned over the first vertebra and overlap the head of a bone engaging fastener extending through the at least one opening positioned over the second vertebra.
In another aspect of the invention, a retainer assembly for an elongated plate is provided. The plate extends between at least two vertebrae and defines a number of openings for insertion of bone engaging fasteners to secure the plate to the at least two vertebrae. The plate includes at least one first fastener bore. The retainer assembly includes a washer that defines at least a first aperture positioned in communication with the at least one fastener bore. A locking fastener extends through the first aperture and has an elongated shank to engage the fastener bore of the plate. The washer is movable along its central axis between a first position where the at least two bone engaging fasteners are inserted through the openings to engage the first and second vertebrae and a second position where a surface of the washer contacts at least the head of the bone engaging fasteners engaged to the first vertebra.
In another aspect of the present invention, a method for applying a compressive load to a number of vertebrae including at least a first vertebra and a second vertebra is provided. The method includes: (a) providing a template having a guide surface and a notch; (b) positioning the template on the second vertebra with the guide surface on an endplate of the second vertebra to locate the template notch on the body of the second vertebra; (c) inserting a pin through the notch of the template into the body of the second vertebra; (d) removing the template; (e) placing a sleeve over the pin; (f) providing a plate having a length extending between a first end and a second end, the plate including a notch on the second end and a number of openings therethrough; (g) placing the plate on the vertebral segment with the sleeve nested in the notch of the plate; (h) fixing the first end of the plate to the first vertebra with bone engaging fasteners extending through the openings positioned over the first vertebra; (i) removing the sleeve from the pin to form a gap between the pin and the notch in the plate; (j) connecting a compression tool to the pin and the plate; and (k) applying a compression load to the vertebral segment with the compression tool until the pin contacts the notch. In one embodiment, the plate includes holes positioned over the first vertebra and slots positioned over the second vertebra. In another embodiment, the method further includes the step of retaining the bone engaging fasteners in the plate with a retainer assembly.
In another aspect of the present invention, there is provided a method for maintaining compression of a spinal column portion. The method includes: (a) providing a plate having a length between a first end and a second end sized to span at least two vertebra, the plate having a pair of holes at the first end positioned over the first vertebra and a pair of slots at the second end positioned over the second vertebra; (b) fixing the first end of the plate to the first vertebra with bone engaging fasteners extending through the pair of holes; (c) securing the second end of the plate to the second plate with bone engaging fasteners extending through the pair of slots; and (d) translating the bone engaging fasteners in the slots to allow settling of the spinal column segment. In one embodiment, the method further includes retaining the bone engaging fasteners in the plate with a retainer assembly.
These and other forms, embodiments, aspects, features, objects of the present invention will be apparent from the following description.